1. Field of the Invention
The invention relates to keyboard encoding and keyboard interface controllers.
2. Description of Related Art
Many different types of electronic systems including general purpose computer systems and calculators, receive manual input through a keyboard. U.S. Pat. No. 4,485,455, issued Nov. 27, 1984 to Boone et al., discloses a calculator that uses a programmed scanning system to provide keyboard encoding. The keyboard comprises an 11 by 4 array of normally open single pole, single throw switches. Each column of the array has four switches, and is connected to a digit driver line. Each row of the array has eleven switches, and is connected to a respective input line to the key input logic of a timing block. The eleven digit driver lines are sequentially scanned, and the four input lines are monitored. The detection of a signal on one of the input lines indicates that a key is depressed in the array, and the location of the key is the cross point of the active driver line and the input line on which the signal was detected.
Although having utility, the scanned keyboard is disadvantageous in some respects. To accommodate larger keyboards, the scanning frequency is increased. The scanning signal is a source of electromagnetic interference ("EMI"), which has become of more concern with the use of higher scanning frequencies. If lower scanning frequencies are used, the keyboard may not be able to react as quickly as desired. Moreover, the power consumption of the keyboard controller is considerable, especially when designed for large keyboards. Power consumption is a particular problem in systems having limited power resources, such as portable personal computers and workstations. Hence, a need has arisen for a novel approach to keyboard encoding.